1. Field of the Invention
The present invention relates generally to a liquid crystal display device, a manufacturing method thereof, and a design method thereof, and more particularly to a liquid crystal display device including a prismatic light guide and a prismatic sheet.
2. Description of the Related Art
A liquid crystal display device includes a liquid crystal display panel. The liquid crystal display panel includes a pair of opposed substrates, that is, an array substrate and a counter-substrate, and a liquid crystal layer which is held between the pair of substrates. A polarizer plate is disposed on an outer surface of each of the array substrate and counter-substrate.
A transmissive liquid crystal display device further includes an area light source unit which is disposed to be opposed to the array substrate-side polarizer plate. The area light source unit includes a light source, and a light guide having a light incidence surface which is opposed to the light source, a light emission surface which is opposed to the array substrate-side polarizer plate, and an opposed surface which is opposed to the light emission surface. In recent years, with a view to improving the efficiency of use of light from a light source, an area light source unit has been put to practical use, which includes a prismatic light guide having prisms formed on at least one of a light emission surface and an opposed surface thereof, and a prismatic sheet disposed on the light emission surface of the light guide.
In the case where the prismatic sheet is formed of a sheet which is fabricated by drawing a plate-shaped polyethylene terephthalate (PET) base material in its planar direction, the prismatic sheet has such characteristics that the prismatic sheet polarizes light that is emitted from the light guide.
In the prior art, there has been proposed a liquid crystal display device wherein a prismatic sheet is selectively used in consideration of the fact that the characteristics of the prismatic sheet vary depending on the position where the prismatic sheet is diced from the PET sheet, and a direction, in which light emitted from the light guide takes a maximum intensity value, is rotated by the prismatic sheet toward a polarization axis of the polarizer plate that is disposed on the outer surface of the array substrate (see Jpn. Pat. Appln. KOKAI Publication No. 2001-166302).
In the method disclosed in the above-mentioned Jpn. Pat. Appln. KOKAI Publication No. 2001-166302, however, the prismatic sheet is disposed such that the prisms of the prismatic sheet are substantially perpendicular to the prisms of the light guide, and the light emitted from the area light source unit interferes with the pattern of the liquid crystal display panel, leading to occurrence of an interference fringe on a display screen.